Preparation And Scintillation Properties Of 12CaO·7Al₂O₃:Ce³⁺ Transparent Ceramics

Scintillator materials which exhibit strong luminescence under high energy beam excitation are widely used in the field of medical diagnosis,security inspection,high energy physics,well logging,etc.In particular,the unique properties of scintillation ceramics make it possible to replace scintillation single crystals.At present,it is still urgent to prepare novel scintillation ceramic materials with high stability,low-cost preparation and good performances.The multifunctional rare earth ions doped 12CaO·7Al₂O₃?C12A7?materials with unique cage structure might be a candidate for scintillator application.In this thesis,C12A7:Ce³⁺ transparent scintillation ceramics have been prepared and the luminescence and scintillation properties have been studied.The main results are described in the following:First,C12A7: x%Ce³⁺ precursor powders were prepared by a solid-state method,then pure C12A7 x%Ce³⁺ ceramics were obtained by sintering these powders at different temperature.It is found that the optimum conditions for the ceramic preparation are the sintering temperature at 1500 oC and 1450 oC.According to the optimized preparation conditions,C12A7:x%Ce³⁺ ceramics with different Ce³⁺ concentrations lower than 0.7% exhibited pure phase.Under 350 nm excitation,the luminescence intensity increases with increasing Ce³⁺ concentration from 0 to 0.7%.Thus,the optimized pure C12A7:0.5% ceramics with strong luminescence can be obtained.In order to increase the number of Ce³⁺ luminescent centers,C12A7:0.5%Ce³⁺ precursor powders were prepared by a combustion method and then pure C12A7:0.5%Ce³⁺ ceramics were obtained by sintering these powders.To further give an insight into the understanding of how encaged anions influence the structural,luminescence and scintillation properties,C12A7:0.5%Ce³⁺ ceramics have been heat-treated under C embedding and H₂ reducing atmosphere.When C12A7: 0.5% Ce³⁺ ceramics were annealed at 1100 oC for 2 h in C embedding reducing atmosphere,the luminescence intensity increased significantly and the emission peak position show a blue-shift.It can be explained by the increased luminescence center and the increased encaged electrons and the weakened crystal field around Ce³⁺.Although the luminescent properties were improved,the increased internal porosity and the poor density of the ceramic sample is unhelpful for the application in scintillator field.When the ceramic samples were annealed at 1300 oC for 3 h in H₂ atmosphere,they still show pure phase,strong luminescence and blue shift of the emission peak position.It is because that Ce4 + was reduced to Ce³⁺ and the sort and amount of encaged anions have been changed in H₂ reducing atmosphere.In particular,part of encaged O2-anions was replaced by encaged H-and OH-and they would lead to the cage distortion and the blue shift of the emission peak.In the meanwhile,the decay time of Ce³⁺ 5d-4f emission of the ceramic samples decreased from 15.2 ns to 14.6 ns,it suggests that C12A7:0.5%Ce³⁺ transparent ceramics might be a potential candidate for the scintillation application.